Conjoined twin

Conjoined twin, formerly called Siamese twin, one of a pair of twins who are physically joined and often share some organs. Fusion is typically along the trunk of the body or at the front, side, or back of the head.

In the case of symmetrical conjoined twins, the children usually have no birthanomalies except at the areas of fusion. In cases where each twin has enough tissue and organs for independent survival, they are often successfully separated by surgery. In the case of nonsymmetric conjoined twins, one is fairly well developed, but the other is severely underdeveloped, often tiny, and dependent on the larger twin for nutrition. The underdeveloped twin may be surgically separated from the larger asymmetric twin in order to save the one better able to survive.

Siamese twins, the term formerly used for these children, originally referred to the conjoined twins Chang and Eng, who were born in 1811 to parents in Siam (now Thailand) and became widely known from their tours in the West. Chang and Eng were joined by a ligament from breastbone to navel.

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May 11, 1811 Meklong, Siam [now Thailand] Jan. 16/17, 1874 Mount Airy, N.C., U.S. congenitally joined twins who gained worldwide fame for their anatomical anomaly. As a result of their fame, the term Siamese twin came to denote the condition of being one of a pair of conjoined twins (of any...

Individuals partially or wholly double, but joined together, are represented by the rare occurrence in man of Siamese twins, so-called from a famous Siamese pair exhibited for many years in the 19th century. The condition consists of identical twins joined by a bridge of tissue through which the circulatory systems communicate. Such twins probably arise by the incomplete separation of a single...

...(MZ) twins. A zygote’s atypical separation into two independent embryonic structures can occur at any of several growth stages. Its incomplete or late division into two cell masses results in conjoined twins, formerly known as Siamese twins. MZ twins usually show a striking physical resemblance to one another. It should be noted that even though hereditary characteristics such as eye...